Nitrogen fixation in biological soil crusts from the Tengger desert, northern China

Abstract

Biological soil crusts (BSCs) are the primary source of soil nitrogen in dry areas. We investigated the nitrogenase activity of three BSC types from the Tengger desert in responses to stimulated precipitation, temperature, and irradiance intensity. In addition, potential seasonal nitrogen fixation by BSCs was estimated using meteorological records. The nitrogenase activity of BSCs ranged from 2.6 to 16.6 mmol m−2 h−1 in this desert, and nitrogenase activity was significantly dependent on crust type, precipitation, and temperature, but not on irradiance. Cyanobacterial–algal crusts showed the highest nitrogenase activity (16.6 mmol m−2 h−1), followed by lichen crusts (6.9 mmol m−2 h−1), and moss crusts (2.6 mmol m−2 h−1). Cyanobacterial–algal crusts demonstrated maximum nitrogenase activity with 1.54 mm of precipitation, while the maximum activity for lichen and moss crusts occurred at 1.83 mm and 0.65 mm, respectively. The optimum temperature for nitrogenase activity ranged from 15 to 30 °C. Based on meteorological data, the potential nitrogen input was estimated to be 3.7–13.2 g m−2 a−1, and the high nitrogen fixation in this region resulted from the perfect match of optimum climate to the favorable environmental factors for BSC nitrogenase activity. This study demonstrated that BSCs are the main nitrogen input source in this temperate desert ecosystem. In particular, cyanobacterial–algal crusts, which are the first colonizers of the desert ecosystem, may mediate the majority of nitrogen fixation to facilitate soil nitrogen accumulation in these infertile soils.